Over recent years, organic electroluminescent elements (thereinafter, also referred to simply as organic EL elements) employing organic materials have been regarded as promising in use as thin, inexpensive large-area full-color display elements of a solid light-emitting type and light source arrays, and therefore active research and development are being conducted.
An organic EL element is a thin film-type element having a first electrode (anode or cathode) formed on a substrate, an organic compound layer (single layer or multilayer), i.e., a light-emitting layer containing an organic luminescent material layered thereon, and a second electrode (cathode or anode) layered on this light-emitting layer. When a voltage is applied to such an organic EL element, electrons are injected into the organic compound layer from the cathode and at the same time, positive holes are injected from the anode. It is known that these electrons and positive holes are recombined in the light-emitting layer and then energy is emitted as light when the energy level returns from the conduction band to the valence band for luminescence from the light-emitting layer.
However, an organic material such as an organic luminescent material used for an organic EL element is vulnerable to moisture and oxygen and tends to degrade in performance due to the moisture and oxygen. Further, since characteristics of an electrode are also degraded drastically in air due to oxygen, generally, a method, in which a sealing layer is provided for the uppermost layer to shield moisture and oxygen in air for prevention of such degradation, is employed.
A number of sealing methods of an organic EL element have been investigated so far, being roughly categorized into a casing-type sealing method and a contact-type sealing method.
The casing-type sealing method is a sealing method, in which an organic EL element is placed in a case to be shielded from the outside and then a certain sealing gas or fluid is filled in the case together with the organic EL element.
On the other hand, the contact-type sealing method is a sealing method using a substrate and a sealing base material, in which the element surface of an organic EL element formed on a substrate is subjected to surface adhesion to a sealing base material such as a glass plate using an adhesive.
In the case of the casing-type sealing method, since a sealing gas or fluid is filled in a case, there have been noted problems such as no possibility of forming a thin type, complicated steps, and unsuitability for mass production.
On the other hand, the contact-type sealing method has advantages such as possibility of responding to a thin type and relative ease of mass production, and therefore, investigations thereon have been conducted in recent years
In the contact-type sealing method, for example, an organic EL element sealed by a sealing film containing a barrier layer and a sealant layer incorporating a thermoplastic adhesive resin is known (for example, refer to Patent Document 1).
Further, in a method using a curable adhesive instead of a thermoplastic adhesive resin, heat-curable and UV-curable adhesives are known. In such a UV-curable adhesive, UV radiation is irradiated to cure an adhesive, and therefore, it is necessary that the substrate irradiation surface be transparent and an irradiated material be one being hardly damaged via UV irradiation. Therefore, the application range has been limited.
In view of these problems, a number of methods employing a heat-curable adhesive have been used because of their advantages in handling and convenience as a manufacturing apparatus.
However, as a problem of a heat-curable adhesive, the following has been found: such an adhesive itself has hygroscopic properties and its moisture content increases with a poor control and storage method; and a sealing member thermally cured using the adhesive becomes problematic in sealing characteristics thereafter.
Therefore, to solve such problems, there are proposed methods in which all members used for sealing are stored in a sealed container of low humidity and low dew point under reduced pressure for dehydration treatment (for example, refer to Patent Documents 1 and 2).
However, such methods require huge storage facilities and thereby cost increase has resulted.
Dehydration of a heat-curable adhesive using a simple method results in a large advantage. As a method of dehydration using a simple method, heating is cited. However, in this method, curing of an adhesive itself is allowed to advance and then its adhesion function is lost. Therefore, it is recognized that any heating method is a method which should be avoided, and then various other methods have been investigated. However, currently, no good method has been found out yet.
In view of such current situations, in a manufacturing method for an organic EL panel in which an organic electroluminescent element is sealed using a sealing method by use of bonding via an adhesive, it has been strongly desired that a manufacturing method for an organic EL panel, in which a simple method is employed and no degradation of the sealing performance occurs even when a sealing substrate is fixed using a heat-curable adhesive and an organic EL panel are developed.
Herein, in the present invention, a state where a first electrode, an organic layer, and a second electrode have been formed on a substrate is referred to as an organic EL element and a state where contact sealing has been carried out using a sealing substrate is referred to as an organic EL panel.